Alloy



Patented June 4, 1940 2 PATENT OFFICE ALLOY Ernest F. Doom and William J. Priestley, New Rochelle, N. Y., assignors to Electro Metallurgical Company, a ginia corporation of West Vir- No Drawing. Application July 1, 193 8,

SerialNo. 216,904

7 Claims.

Columbium and tantalum are useful ingreclients in many steels, notably the chromium steels. In the manufacture of such steels it is ordinarily most convenient, efficient, and economical to add columbium-tantalum group metal (by which is meant columbium or tantalum or mixtures thereof) in the form of lumps of a ferroalloy. For most purposes, such ferroalloy should contain as little carbon as possible and in no event more than 1% carbon, because columbium and tantalum form exceedingly stable and inert carbides, and it is generally the non-carbide columbium or tantalum that is desired. A typical ferrocolumbium contains about 55% columbium, about 0.5% carbon, about 7% silicon, and the remainder iron and incidental impurities. A moderately high silicon content, say 5% to is advantageous.

Although ferrocolumbium is a very useful material that has been successfully employed in the manufacture of many tons of steel, it has certain properties which are undesirable in a material to be introduced into steel baths.

The melting point of ferrocolumbium is relatively high (about 1950 C. to 2200 C. depending on the composition) and this fact makes it somewhat diflicult to dissolve the alloy in a steel bath rapidly and without serious oxidation of the columbium. Ferrotantalum has a melting point even higher than that of ferrocolumbium.

Ferrocolumbium and ferrotantalum are friable, and crushing operations produce an undesirably large proportion of fines and dust having considerably less commercial value than granular and lump alloy.

7 It is an object of this invention to provide anew ferroalloy containing columbium-tantalum group metal and having a lower melting point and 'better crushing characteristics than have heretofore been attainable in commercially useful ferrocolumbium and ferrotantalum alloys.

The objects of the invention are achieved by forming a ferroalloy containing both chromium and columbium-tantalum group metal, the total amount of both, chromium and columbium-tantalum group metal amounting preferably to between 40% and 90% of the alloy.

As little as one part of chromium for each twenty parts of columbium-tantalum group metal is suflicient to impart a valuable improvement to the properties of the new alloy. Larger proportions of chromium may be, and preferably are, used; but the alloy should contain at least one part of columbium-tantalum group metal for each twenty parts of chromium. In the majority of instances, a ratio of columbium-tantalum group metal to chromium between :1 and 1:15 will be quite satisfactory. In general, the preferred minimum amounts of chromium and columbiumtantalum group metal are each, and normally neither metal need exceed 50%. For many purposes, the most useful alloys are those containing approximately equal amounts of chromium and columbium-tantalum group metal.

The iron content of the new alloy usefully affects the properties of the alloy and also contributes to the ease of manufacture of the material; but the iron content should not greatly exceed 60%, and is preferably much less.

The carbon content should not exceed 1%, and a percentage below 0.25% is preferred for the reasons indicated above.

A moderate silicon content, not exceeding 20% and preferably within the range of 3% to 8%, is desirable but not essential. substituted for a part or all of the silicon, but of the two silicon is preferred. Manganese or nickel or mixtures thereof may be substituted for part of the iron. Small amounts of other elements such as titanium, copper, and tin may be introduced or may enter as incidental impurities without adversely affecting the usefulness of the alloy.

Typical examples of the alloy of the invention have the following compositions: (I) 33.9% Cr, 32.9% Cb, 2.2% Ta, 0.5% Ti,,6.7% Si, 2% Mn,

v 0.3% Ni, 0.18% C, remainder substantially iron;

(II) 28.6% Cr, 43.2% Cb, 5.4% Si, 0.26% C, remainder substantially iron; '(III) 32.8% Cr, 39.8% Cb, 1.4% Ta, 6% Si, 0.38% C, remainder substantially iron. These alloys may be crushed to lumps between 1.5 and 0.03 inch in diameter without producing more than about 7% of material smaller than 0.03 inch. This represents about one-half the proportion of fines normally produced in crushing ferrocolumbium. The melting points of these new alloys (solidus) fell within the range of 1620 to 1750 C. The range between the solidus and liquidus is about 200 C. wide, and is narrower than that for ordinary ferrocolumbium.

The alloy of this invention may be used as an addition agent for adding chromium and columbium-tantalum group metal simultaneously to any metal bath, either ferrous or non-ferrous. The preferred compositions, containing approximately equal proportions of chromium and 00-, lumbium-tantalum group metal, are particularly valuable in the manufacture of the ferritic and austenitic steels containing 6% to"30% chro- Aluminum may be mium, a small content of carbon, and enough 00- lumbium-tantalum group metal to combine with all, or nearly all, of the carbon.

The alloys of the invention may be made by a remelting procedure using, for instance, low car bon ferrochromium and low carbon ferrocolumbium. But this method is not economical, because it requires three separate manufacturing steps each requiring equipment, time, power, and involving slag losses and adventitious increases in carbon content.

Another process for making these alloys comprises the simultaneous, reduction of the ores of chromium and columbium with carbon, silicon, or aluminum. One of the serious objections to this process is that either poor recovery of metallic ingredients or an impure or otherwise unde known processes, the reductions referred to can be effected in the absence of any substantial amount of carbon. As a result, alloys containing less than 0.25% carbon may readily be obtained.

In the following description of the process, reference will be made to columbium alone, for the sake of conciseness; but it will be understood that tantalum and mixtures of columbium and tantalum may be substituted for the columbium.

The gangue content of the usual chrome ores contributes more than the gangue content of the usual columbium ores to an increase in slag content. For this reason it is preferred to start with the chromium in metallic form and to reduce columbium alone in the process.

According to a preferred procedure, a bath of molten low-carbon ferrochromium-silicon or chromium-silicon alloy is formed and provided with a slag, preferably .basic, and an oxidic columbium ore or compound is added to the bath through the slag. As columbium is reduced, the metal joins the bath, and silicon is oxidized and joins the slag. Although ordinarily the silicon content of the ferrochrome-silicon alloy will be selected so that the refining effect of the columbium-tantalum group oxide will be just sufficient to reduce the silicon content to that desired in the final alloy, part of the silicon may be added to the bath as silicon metal or silicon alloyed with one or more of the metals desired in the final composition.

Alternatively, a bath of molten low-carbon columbium-silicon or ferrocolumbium-silicon alloy may be treated, in similar fashion, with oxidic chromium ore or compound. Part of the silicon may be added in the form of silicon metal, ferrosilicon, chromium-silicon, or ferrochromium-= silicon,

Another procedure comprises forming a small starting bath of any one or more of the metallic constituents of the desired alloy, progressively feeding into this bath a mixture containing the oxidic compound and the silicon-containing alloy,

and heating the bath to keep it molten.

- finely ground, intimately mixed, and ignited.

External heating, or a suitable accelerator such as sodium nitrate, or both, may be needed in some instances to sustain the reaction; but the exothermic reaction will in any event contribute heat for the production of a molten bath.

In any of these procedures, iron may be added before, during, or after the reaction of silicon and oxidic compound, to produce either a ferroalloy or a steel. If an alloy steel is desired, an economical and simple procedure is to feed a mixture of the silicon alloy and oxide described above into a slag-covered molten bath of iron or steel.

The slags obtained in these operations will of course contain oxides of both chromium and columbium, but deliberate simultaneous addition of substantial amounts of the oxide of more than one of these elements is to be avoided, because such addition will increase the slag losses of valuable metal. 7

The slags containing oxides of columbium and chromium are preferably smelted with silicon or with a mixture of carbon and silica to produce a ferrochromiumrcolumbium-silicon alloy, low in carbon, which can be substituted for part of the chromium-silicon, columbium-silicon, ferrochromium-silicon, or ferrocolumbium-silicon mentioned in the foregoing description. Alternatively, the slag may be smelted to a high carbon alloy and then refined or remelted to lower the carbon and raise the silicon content.

In a typical experiment to produce an alloy in accordance with this invention, one thousand pounds of columbite and five hundred and ninety pounds of ferrochromium-silicon were ground to pass an 8 mesh screen (2.36 mm. opening) and the starting materials and products were as follows:

Fe-Gr-Si Fe-Cr-Ob (Jolumbite alloy alloy Mag 61.8% 0mm 34.6% Cr 28.6% ("r 0.3%.(::

5.1% T8205 50.1% Si 432% Ch 7.:- OM0 0.7% Ta 14.1% (:10 14.3% Fe 18.1%l Fe 5.4% Si 5.8% FeO 0.04% G 1.8% Mn 0.26% C 2.2% MnO 64% of the columbium and 90% of the chromium were recovered in metallic form.

Although in the foregoing description preferred conditions have been described in some detail, economic and other practical considerations .may on occasion dictate a departure from such Accordingly, the detailed description conditions. is to be regarded as illustrative of the invention and not as imposing limitations not required by the state of the art and the scope of the claims. We claim: 1. Alloy containing chromium, columbiumtantalum group metal, iron, carbon, and silicon; the percentages of chromium and columbium being at least 20% each and the combined percentages of chromium and columbium being at least 50%, the silicon being less than the carbon being less than 1%, and the remainder being iron and incidental impurities.

2. Alloy as defined in claim 1, wherein the percentages of columbium and chromium are approximately the same.

3. Alloy containing 20% to chromium and 50% to 20% columbium, the total percentage of columbium and chromium being between 50% and 3% to 8% silicon; carbon in an amount not exceeding 1%; remainder iron and incidental impurities.

4. Alloy as defined in claim 3, wherein the percentages of columbium and chromium are approximately the same.

5. As a prealloy to be added to a steel bath, an alloy having approximately the composition: 35% chromium; 35% columbium; 6% silicon; 0.2% carbon; remainder iron and incidental im- 20 purities.

6. Chromium-base alloy containing chromium,

columbium-tantalum group metal, iron, carbon, and silicon; the chromium content being more than 50%, the columbium percentage being at least one-twentieth of the chromium percentage but less than 50%, the silicon content being less than 20%, the carbon content being less than 1%, and the remainder being iron and incidental impurities.

'7. Columbium-tantalum group metal alloy containing columbium-tantalum group metal, chromium, iron, carbon, and silicon; the percentage of columbium-tantalum group metal being between 25% and the percentage of chromium being at least one-twentieth of the percentage of said columbium-tantalum group metal but less than 20%, the silicon content being less than 20%, the carbon content being less than 1%, and the remainder being iron and incidental impurities.

ERNEST F. DOOM.

WILLIAM J. PRESTLEY. 

